Implement a method to invalidate the cache

[simone-viozzi]

As discussed in #217 we need a method / mechanism to invalidate the cache for specific paths.

This is needed because, if the user move / delete a file, and it is still in the cache, the library will continue to 'think' that the file is still in the old location. Leading to unexpected behaviors.

This mechanism is needed in the mv and rm_file method.